This invention relates to the stabilization of railroad vehicles and more particularly to a method of eliminating truck hunting in rail vehicle trucks.
The conventional freight car truck consists of three structural members: a bolster and two side frames. The bolster has a center plate bowl which supports the freight car body. At the ends of the bolster there are flat surfaces which receive the top surface of resilient means which supports the ends of the bolster. The side frames have a mating surface for receiving the opposite ends of the resilient members. There are jaws on the extreme ends of the side frames for receiving an adapter arrangement which connects to the bearings of the axle/wheel sets. The wheel sets consist of outboard roller bearings and steel wheels pressed onto an axle. The steel wheels have a special tread contour where they contact the rail.
Brake rigging which is supported by the truck members provides the braking force when the brake linkage is actuated. The primary elements of the brake linkage are the brake beams, levers and brake shoes. The brakeshoes are attached to the ends of the brake beams and form the interface at the wheel when the braking force is applied to the brake linkage.
Truck hunting is a dynamic instability inherent in the railroad freight car truck described above aggrevated by the interaction between the rail head and the contour of the wheel tread and transferred through the side frame and bolster members of the trucks. At a critical speed, depending primarily upon the weight of the car body, the condition of the rail and wheel tread, and the damping and spring rate of the suspension, the truck vibrates due to a parallelogramming action described below.
Prior solutions to the problem of truck hunting are concerned with maintaining the rail car truck in a square or non-parallelogrammed position by stiffening or damping the truck itself.
The problem is recognized and described in U.S. Pat. No. 4,103,623 and overcome by placing a friction member between the truck side frames and bolster which tends to resist and control the parallelogramming motion of the truck.
U.S. Pat. No. 4,103,624 also addresses the problem of truck hunting. An integral H-frame truck is disclosed which increases the speed at which the instability that results in truck hunting occurs.
U.S. Pat. No. 3,687,086 and U.S. Pat. No. 3,714,905 disclose railway trucks having wedge means between the truck bolster and side frame to maintain truck squareness and thereby reduce wheel wear. The truck hunting phenomenon is not specifically described, however.